Portable electronic devices such as a camcorder, a mobile phone and a laptop computer have been rapidly improved in compactness and weight reduction. As a driving power source for these devices, non-aqueous electrolyte secondary cells, which have high energy density and high capacity, are widely used.
In recent years, non-aqueous electrolyte secondary cells have also been used as the driving power source of electric tools, electric vehicles, and the like. In such uses, excellent cycle characteristic is required over a wide temperature range from low to high temperature.
Techniques of such a non-aqueous electrolyte secondary cell are described in the patent documents 1 to 10.
[Patent Document 1]
Japanese Patent Application Publication No. H8-111239
[Patent Document 2]
Japanese Patent Application Publication No. 2002-270225
[Patent Document 3]
Japanese Patent Application Publication No. 2008-98107
[Patent Document 4]
Japanese Patent Application Publication No. 2002-33123
[Patent Document 5]
Japanese Patent Application Publication No. S60-65479
[Patent Document 6]
Japanese Patent Application Publication No. 2000-294294
[Patent Document 7]
Japanese Patent Application Publication No. 2010-113804
[Patent Document 8]
Japanese Patent Application Publication No. H11-135107
[Patent Document 9]
Japanese Patent Application Publication No. H6-275321
[Patent Document 10]
Japanese Patent Application Publication No. 2007-220455
Patent Document 1 discloses a technique in which the ratio of electrolyte amount and charge-discharge capacity is set to 0.0064 cc/mAh or more. The document states that this technique can provide a coin-type secondary cell that is capable of preventing the occurrence of defects unique to the thin shape of the cell.
Patent Document 2 discloses a technique in which, in a lithium secondary cell with a volumetric capacity density of 400 Wh/L or more, the total amount Q of an electrolyte solution in the cell is regulated as (Vx+0.4 Vy)≦Q≦(Vx+0.8 Vy) wherein Vx denotes the total volume of voids in a polymer membrane and positive and negative electrodes, and Vy denotes the volume sum of a space between the electrodes and the polymer membrane, a space between an inner wall of a cell case and a side wall of the electrode plates consisting of the electrodes and the polymer membranes, and voids in the cell (top and bottom of the electrode plates). The document states that this technique can ensure high capacity and long-life characteristics.
Patent Document 3 discloses a technique in which the amount of organic solvents per Ah of cell capacity is 6 to 8 g/Ah, and the facing area between the negative electrode active material containing layer and the positive electrode active material containing layer per gram of the organic solvents is regulated to 130 to 290 cm2/g. The document states that this technique can provide a non-aqueous electrolyte cell that excels in rapid charge performance.
Patent Document 4 discloses a technique in which the volume of electrolyte per unit cell discharge capacity (Ah) is 3 to 7 g, lithium tetrafluoro borate is used as a lithium salt, and the concentration of the lithium salt is set to 1.5 to 4 M. The document states that this technique can provide a film-packaged non-aqueous electrolyte cell having excellent safety without electrolyte leakage and cell swelling.
Patent Document 5 discloses a technique in which a value of an electrolyte amount divided by a positive electrode capacity is 3 μL/mAh or higher in a lithium secondary cell using a transition metal chalcogen compound as a positive electrode active material and using lithium or lithium alloy as a negative electrode active material. The document states that this technique can improve charge-discharge cycle characteristics.
Patent Document 6 discloses a technique in which, in a non-aqueous electrolyte secondary cell using lithium manganese oxide as a positive electrode active material, when the sum of the void volume, which is calculated from porosities of negative and positive electrodes and a separator, is defined as 1, the amount of a non-aqueous electrolyte solution is 0.8 to 1.5. The document states that this technique can improve cycle characteristics of the non-aqueous electrolyte secondary cell using lithium manganese oxide as a positive electrode active material under high temperature condition.
Patent Document 7 discloses a technique in which the amount (by volume) of a non-aqueous electrolyte solution is set to 0.9 times or higher and 1.6 times or lower of the total volume of voids in a separator and positive and negative electrodes. The document states that this technique can further suppress capacity decrease during repeated charge-discharge cycles.
Patent Document 8 discloses a technique in which, in a negative electrode using graphitic carbon as a negative electrode active material, the impregnation rate of an electrolyte solution is set to 70 to 90%. The document states that this technique can provide a lithium secondary cell having excellent cycle characteristics and less capacity deterioration involved in charge-discharge operations.
Patent Document 9 discloses a technique regarding a lithium secondary cell. The cell comprises: a positive electrode comprising, as a positive electrode active material, a lithium metal compound mainly containing at least one metal selected from cobalt, nickel, manganese, vanadium, titanium, and molybdenum or iron; carbon material that is powder having 0.340 nm or less of diffraction peak (d002) of (002) plane in the graphite structure by X-ray diffraction; and a non-aqueous electrolyte solution. In this cell, the amount of the non-aqueous electrolyte is 7 cm3/Ah relative to cell discharge capacity. The document states that this technique can provide a lithium secondary cell having high capacity and excellent cycle life.
Patent Document 10 discloses a technique in which, the amount of non-aqueous electrolyte solution is set to 1.3 to 1.8 μL per 1 mAh of discharge capacity. The document states that this technique can realize a non-aqueous electrolyte secondary cell having excellent reliability during high-temperature storage, without deteriorating cycle characteristics even when the cell capacity and energy density are high.
However, even with any of the above technologies, there is a problem that excellent cycle characteristic is not necessarily obtained over a wide temperature range from low to high temperature.